Magnetic head supporting mechanism, magnetic head apparatus, head actuator using the magnetic head apparatus and magnetic recording apparatus

ABSTRACT

An object of the present invention is to provide a hard disk drive or related apparatus in which a possibility of head crash can be reduced to minimum even if the apparatus receives an external impact during the operating state. To achieve the object, according to the present invention, in a suspension including a load beam to which a magnetic head slider is to be attached and a head arm continuously joined to the load beam, a dummy weight is attached to the rear end of the head arm, and a attachment position of a joining member for joining a portion including the magnetic head slider, the load beam, the head arm and the dummy weight with a swing portion of a voice coil motor is provided at a position in the vicinity of the center of mass of that portion.

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] The present invention relates to a suspension apparatus, amagnetic head apparatus, a head actuator and a magnetic recordingapparatus, and particularly to a suspension apparatus, a magnetic headapparatus, a head actuator and a magnetic recording apparatus that haveimproved impact resistance in operating state.

[0003] 2. Related Background Art

[0004]FIG. 6 is a drawing schematically showing a prior art magneticrecording apparatus. As shown in FIG. 6, the magnetic recordingapparatus 101 is provided with a magnetic disk 102 serving as arotatable magnetic recording medium and an actuator 104 for moving amagnetic head, which is floating (or hovering) above the magnetic disk102, in a radial direction of the magnetic disk 102. The magneticrecording apparatus 101 is further provided with a movable coil 105 anda magnetic circuit 106, which constitute a voice coil motor (which willbe referred to as a VCM hereinafter).

[0005] In the magnetic recording apparatus 101 having theabove-described structure, a servo signal (i.e. position information)that has been written in the surface of the magnetic disk in advance isread by the magnetic head 103, and the magnetic head 103 is movedrelative to the surface of the magnetic disk 102 based on the readinformation. Specifically, electric power is supplied to a movable coil105 provided at the opposite end of the magnetic head 103, so that aforce is generated in a magnetic circuit 106 in the directions indicatedby an arrow 107. Thus, the magnetic head 103 is moved to a target track(or a target position).

[0006]FIG. 7 is a drawing schematically showing how the magnetic headapparatus is disposed in relation to the magnetic disk. As shown in thisdrawing, a load beam 109 is provided at the intermediate portion of themagnetic head 103. One end portion of the load beam 109 is secured to abase plate 108 that makes a junction with a head arm 115 in an actuator104. On the other end portion of the load beam 109, there is provided aslider 110 attached thereto. In addition, an elastic spring portion isprovided at the boundary 111 of the load beam 109 and the base plate108.

[0007] In the process of writing information in the magnetic disk 102with the above-described magnetic head, the magnetic disk 102 is rotatedat several thousands revolutions per minute. The writing and otherprocesses are performed under the state in which the rotation of themagnetic disk 102 is maintained. During that, the magnetic head 103 canbe maintained in a state spaced apart from the magnetic disk 102 by apredetermined minute spacing in accordance with a balance between apressure caused by air involved in the rotation of the magnetic disk 102and a load exerted by a spring or other element (not shown) disposed onthe actuator 104. This predetermined spacing thus maintained enablestable writing of information or other processes.

[0008] The capacity and recording density of hard disk drives have beenincreased rapidly, and hard disk drives with areal densities of morethan 40 gigabits per square inch have been recently announced. Inaddition, the price of the hard disk drives per unit storage capacityhas been reduced rapidly. In view of such situations, applications ofhard disk drives other than conventional applications such as forservers or computers are contemplated. Specifically, applications asstorage devices for digital still cameras or portable terminals such ascellular phones are contemplated.

[0009] Portable terminals including portable personal computers (whichare sometimes called notebook sized personal computers) are required tobe compact in the size and thickness and to be impact proof. However,generally speaking, the hard disk drive is vulnerable to impacts. Thisis because the magnetic head must maintain, as described in the above, aminute spacing from the magnetic disk rotating at a high rate during theprocess of writing information on the hard disk drive. In other words,if the hard disk drive receives an impact under an operating state suchas writing, there is a considerable possibility that the magnetic headwould collide with the magnetic disk that is rotating at a high rate tocause so-called head-crash.

[0010] As a solution for such a problem, Japanese Patent Application No.9-82052 discloses, for example, a structure in which a load is given toan extension formed as a part extending from a load beam so that thecenter of impact acceleration created in a slider due to an externallyapplied impact would be shifted to the rotation center of the slider.Furthermore, Japanese Patent Application Laid-Open No. 8-102159 and No.2001-57032 disclose a structure in which a limiter for limiting swing ofa slider caused by an externally applied impact is provided with respectto the direction of the swing to reduce the amplitude of the swingmovement. However, these solutions are directed to reduction of theswing that would be caused under conditions of ordinary use, but theycannot cope with situations, such as dropping of the hard disk drive tothe ground or floor, which should be taken into consideration in thecase of portable devices.

[0011] In other words, conventional hard disk drives have been designedunder a presumption that they are used in a standstill state. Therefore,under the present circumstances, no consideration is made for behaviorsof a magnetic head, a suspension and other parts of a hard disk drive onthe occasion of receiving a strong impact.

SUMMARY OF THE INVENTION

[0012] The present invention has been made in view of theabove-described situations. An object of the present invention is toprovide a suspension, a magnetic head, a head actuator and a magneticrecording apparatus in which a risk of the head-crash is reduced tominimum, even when they receive a strong impact.

[0013] In view of the above-mentioned problems, according to the presentinvention, there is provided a magnetic head supporting mechanism or asuspension apparatus comprising a load beam adapted to be attached witha magnetic head slider at one end and a head arm, the tip end of thehead arm being joined with the other end of the load beam, wherein adummy weight is attached to the rear end of the head arm,

[0014] the center of mass of a portion including all of the magnetichead slider, the load beam, the head arm and the dummy weight coincideswith the center of swing movement of the head arm in a radial directionof a recording medium and with the center of swing movement of the headarm in a direction perpendicular to a recording surface of the recordingmedium.

[0015] Specifically, in the magnetic head supporting mechanism or thesuspension apparatus according to the invention, the attachment positionof a joining member for joining the portion including all of themagnetic head slider, the load beam, the head arm and the dummy weightwith a swing portion of a voice coil motor would be arranged at aposition in the vicinity of the center of mass of the portion includingall of the magnetic head slider, the load beam, the head arm and thedummy weight, and said portion would be supported by a pivot pin at saidcenter of swing movement of the head arm in the perpendicular direction.

[0016] In the above-described head supporting mechanism or thesuspension apparatus, it would be preferable that the load beam and thehead arm be joined in such a way that their center lines in thelongitudinal direction coincides with each other, and the attachmentposition of the dummy weight and the attachment position of the joiningmember for joining the voice coil motor for swinging the head arm in theradial direction of the recording medium with the head arm berespectively arranged to be symmetrical with respect to said centerline. In addition, it would be preferable that the load beam and thehead arm be constructed as a single member. It would also be preferablethat the load beam and the head arm be made of a resin.

[0017] Furthermore, in view of the above-mentioned problems, there isprovided according to the present invention a magnetic head apparatuscomprising a magnetic head slider, a load beam adapted to be attachedwith a magnetic head slider at one end, and a head arm, the tip end ofthe head arm being joined with the other end of the load beam, wherein adummy weight is attached to the rear end of the head arm, the center ofmass of a portion including all of the magnetic head slider, the loadbeam, the head arm and the dummy weight coincides with the center ofswing movement of the head arm in a radial direction of a recordingmedium and with the center of swing movement of the head arm in adirection perpendicular to a recording surface of the recording medium.

[0018] Specifically, in the magnetic head apparatus according to theinvention, the attachment position of a joining member for joining theportion including all of the magnetic head slider, the load beam, thehead arm and the dummy weight with a swing portion of a voice coil motorwould be arranged at a position in the vicinity of the center of mass ofthe portion including all of the magnetic head slider, the load beam,the head arm and the dummy weight, and said portion would be supportedby a pivot pin at said center of swing movement of the head arm in theperpendicular direction.

[0019] In the above-described magnetic head apparatus, it would bepreferable that the load beam and the head arm be joined in such a waythat their center lines in the longitudinal direction coincides witheach other, and the attachment position of the dummy weight and theattachment position of the joining member for joining the head arm withthe voice coil motor for swinging the head arm in the radial directionof said recording medium be respectively arranged to be symmetrical withrespect to said center line. In addition, it would be preferable thatthe load beam and the head arm be constructed as a single member. Itwould also be preferable that the load beam and the head arm be made ofa resin.

[0020] Still further, according to the present invention, there isprovided a head actuator comprising a magnetic head including a magnetichead slider, a load beam adapted to be attached with the magnetic headslider at one end and a head arm the tip end of which is joined with theother end of said load beam, and a swing portion of a voice coil motorhaving a support arm that swingably supports the magnetic head, whereina dummy weight is attached to the rear end of the head arm, the head armis joined with the support arm via a joining member, a portion includingthe magnetic head slider, the load beam, the head arm and the dummyweight is biased, at the center of mass of said portion, in a directionaway from the support arm by a pivot pin provided on the support arm, sothat said portion is supported in such a way that it is spaced from saidsupport arm by a predetermined distance with its substantiallyhorizontal state being maintained.

[0021] In the above-described head actuator, it would be preferable thatthe load beam and the head arm be joined in such a way that their centerlines in the longitudinal direction coincides with each other, and theattachment position of the dummy weight, the attachment position of thejoining member and the biasing position of the pivot pin be respectivelyarranged to be symmetrical with respect to said center line. It would bealso preferable that the joining member be made of an elastic member. Inaddition, it would be preferable that the elastic member be a leafspring having a U-like shape, the round portion and the end portions ofthe leaf spring be arranged along said center line, and the roundportion be secured to either one of the support arm and the head arm,and the end portions be secured to the other one of the support arm andthe head arm. It would also be preferable that the load beam and thehead beam be constructed as a single member made of a resin.

[0022] Furthermore, in view of the above-described problems, a magneticrecording apparatus according to the present invention may be equippedwith a magnetic head apparatus according to one of the above-describedmodes or a head actuator according to one of the above-described modes.

BRIEF DESCRIPTION OF THE DRAWINGS

[0023]FIG. 1 is a cross sectional view schematically showing theprincipal portion of a magnetic disk apparatus according to a firstembodiment of the present invention.

[0024]FIG. 2 is a top view showing the principal portion shown in FIG.1.

[0025]FIG. 3 is a drawing showing the general structure of a mountportion on a VCM (voice coil motor) according to a modification of thefirst embodiment.

[0026]FIG. 4 is a cross sectional view schematically showing theprincipal portion of a magnetic disk apparatus according to a secondembodiment of the present invention.

[0027]FIG. 5 is a top view showing the principal portion shown in FIG.4.

[0028]FIG. 6 is a drawing schematically showing the structure of aconventional magnetic recording apparatus.

[0029]FIG. 7 is a drawing for illustrating how the magnetic headapparatus is disposed in relation to the magnetic disk.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

[0030] (First Embodiment)

[0031]FIG. 1 is a side view schematically showing the principal portionof a magnetic disk apparatus as a first embodiment of the presentinvention. FIG. 2 is a top view showing the same principal portion ofthe magnetic disk apparatus. The magnetic disk apparatus according tothis example is an apparatus that is capable of writing information onboth sides of a magnetic disk. In addition, in order to facilitateunderstanding of the invention, only the principal portion isillustrated in these drawings, and illustrations of a magnetic disk andcomponents such as a flexure and a plate are omitted. In all of thedrawings that will be referred to in the following, the same componentswill be designated by the same reference characters.

[0032] Referring to the drawings, at the tip end of each head arm 15, aload beam 9 is supported by the head arm 15 via a plate (which is notshown in the drawings). The load beam 9 is supported by the head arm 15at one end thereof, and the load beam 9 supports a magnetic head slider3 at the other end. The magnetic head slider 3 is so supported that arecording/reproducing element end (not shown) formed on the slider isopposed to a magnetic recording medium. Dummy weights 17 are attached tothe rear end portion of the head arm 15. In the arrangement according tothis embodiment, the load beam 9 and the head arm 15 are connectedtogether in such a way that the center lines of them coincide with eachother (i.e. they are coaxial).

[0033] The magnetic head slider 3, the load beam 9, the head arm 15 andthe dummy weights 17 are supported, as an integral portion, by a swingportion 5 of a voice coil motor (VCM) (not shown). Specifically thisintegrated portion of the magnetic head slider 3 and other parts aresupported by a support arm 20 extending from the swing portion 5 of theVCM via a leaf spring 16 having a U-like shape serving as a joiningmember provided on the head arm 15 at a position about the position ofcenter of mass of the integrated portion including the above-mentionedmagnetic head slider and other parts with respect to the longitudinaldirection. In connection with this, the dummy weights 17 are provided asdivided members so that they would not interfere with the arrangement ofthe support arm 20 and other parts and the weight (or mass) would beequally distributed with respect to the center line of the load beam 9and the head arm 15.

[0034] On the support arm 20, there is provided pivot pins 18 for urgingthe integrated portion including the magnetic head slider and the otherparts so that the integrated portion would be spaced apart from thesupport arm 20. The urging positions 21 of the pivot pins 18 are adaptedto approximately coincide with the center of mass of the integratedportion including the load beam 9, the head arm 15 and the dummy weights17 etc. with respect to the longitudinal direction and to correspond toportions located equidistant from the center line of the magnetic headslider and other parts. More specifically, the leaf spring 16 having aU-like shape is arranged in such a way that the round portion 16 a atthe center thereof is oriented to the tip end direction of the head arm15 and the end portions 16 b of the leaf spring 16 are oriented to therear end direction of the head arm 15, so that the round portion 16 a isfixed to the support arm 20 and the end portions 16 b are fixed to thehead arm 15.

[0035] With the above-described structure, the integrated portionincluding the magnetic head slider and other parts is supported at aposition in the vicinity of its center of mass by the leaf spring 16having a U-like shape in such a way that it is spaced apart from thesupport arm. Therefore, the integrated portion including the magnetichead slider and other parts is supported under a horizontally orientedstate at any time. In other words, even when a strong impact is appliedto the apparatus from the outside, the horizontally oriented state ofthe integrated portion including the magnetic head slider and otherparts is maintained without a particular change and vibrated only in thevertical direction, since the center of mass of the portion includingthe load beam 9, head arm 15 and dummy weights 17 is coincide with theurging position 21 of the pivot pins 18.

[0036] If a reactive force created at the pivot pins 18 by the U-shapeleaf spring 16 is sufficiently larger than a force created by a givenimpact acceleration and a weight of the integrated portion including themagnetic head slider and other parts, movement of the integrated portionincluding the magnetic head slider and other parts can be suppressed, sothat the possibility of collision of the magnetic head slider and themagnetic disk can be reduced to minimum. In addition, if the rigidity ofthe head arm or other parts is sufficiently high in relation to anapplied acceleration, deformation of the head arm or other parts withrespect to the vertical direction can be suppressed satisfactorily. Inthis case, the possibility of the collision of the magnetic head sliderand the magnetic disk can be further reduced.

[0037] In this embodiment, the U-shape leaf spring 16 is attached to thesupport arm 20 and the head arm 15 by spot welding or by using anadhesive. Thus, the positions at which the leaf spring 16 is attached tothe respective arms are different in the horizontal direction.Therefore, a moment load will be generated about the pivot pins 18 inthe rotation direction for causing the magnetic head slider to approachthe surface of the magnetic disk.

[0038] In conventional structures, a magnetic head slider is biasedtoward the surface of a magnetic disk by an elastic spring portionprovided between an arm head and a load beam. With the implementation ofthe present invention, the leaf spring that has been conventionally usedmay be omitted. The leaf spring conventionally used suffers from a riskthat a rotational vibration of the magnetic head slider and other partsmay be generated about the leaf spring, when an external impact isexerted. However, if the leaf spring is omitted, causes of such avibration can be reduced.

[0039] In the structure according to this embodiment, theabove-mentioned rotation moment is cancelled by adjustment of the weightof the dummy weights 17. On the other hand, it is also possible toincrease or reduce the rotation moment by adjusting the weight of thedummy weights 17. When the center of mass of the magnetic head sliderand other parts is fixed to a predetermined position, high precisionassembling is generally required.

[0040] However, according to the present invention, it is possible toshift the center of mass to a predetermined position after assembling ofthe head slider and other parts to the VCM etc. if a structure thatallows adjustment of the position or weight of the dummy weight(s) isadditionally provided. Alternatively, if the pivot pins are adapted tobe slidable on the support arm in the direction of the head arm, it iseasy to adjust the pivot pins to support the center of mass. Therefore,with the present invention including the above-described structure, itis possible to facilitate efficiency of the assembling process of thehard disk drive.

[0041] The structure that is generally referred to as a suspensioncorresponds, in the present invention, to the portion composedessentially of the load beam, the head arm and the dummy weights. Thestructure referred to as a magnetic head corresponds to the portioncomposed of the suspension and the head slider etc. The structurereferred to as a head actuator corresponds to the portion composed ofthe magnetic head and the VCM that are coupled together.

[0042] (Modification)

[0043] A modification of the first embodiment will be described. In thismodification, the leaf spring having a U-like shape is fixed to thesupport arm by a nut or the like. FIG. 3 is a drawing showing that fixedstate, in which only the round portions 16 a of the U-shape leaf springsare illustrated in the drawing for the sake of simplicity. The swingportion 5 of the VCM for swinging the head slider(s) and other parts isrequired to be supported by a rotation shaft 26 via a ring 25.Generally, the arm portion 20 of the swing portion 5 is fixed to abearing case 27 that is rotatably supported by the rotation shaft 26 bya nut 28 or the like.

[0044] In this modification, the round portion 16 a of the U-shape leafspring 16 is disposed between the bearing case 27 and the arm portion20, so that the round portion 16 a is secured between them. The pivotpin 18 is provided on the arm portion 20 and the head arm, the dummyweights and the ends of the U-shape leaf spring are disposed in such away that they do not interfere with the bearing case and the armportion. With such a structure, the magnetic head slider and other partscan be easily attached to the VCM. Therefore, it is possible to enhanceefficiency of the assembling process of the hard disk drive still more.

[0045] (Second Embodiment)

[0046]FIG. 4 is a cross sectional view schematically showing theprincipal portion of a magnetic disk apparatus as a second embodiment ofthe present invention. FIG. 5 is a top view of the same principalportion. The magnetic disk apparatus according to this example is anapparatus that is capable of writing information on both sides of amagnetic disk. In addition, in order to facilitate understanding of theinvention, only the principal portion is illustrated in these drawings,and illustrations of a magnetic disk and components such as a flexureand a plate are omitted.

[0047] The structure of this embodiment is the same as that of the firstembodiment except for the arrangement of a support arm 20 and, inconnection with this, the arrangement of leaf springs 16 having a U-likeshape and pivot pins 18. Namely, the structure of magnetic head sliders3, load beams 9, head arms 15 and dummy weights 17 are the same as thestructure of the corresponding parts in the first embodiment. Therefore,the following specific description will be directed mainly to theportions that are different from those in the first embodiment.

[0048] In this second embodiment, a single support arm 20 is used, andeach leaf spring 16 having a U-like shape is arranged in such a way thatthe round portion 16 a at the center thereof is oriented to the rear enddirection of the head arm 15 and the end portions 16 b of the leafspring 16 are oriented to the tip end direction of the head arm 15, sothat the round portion 16 a is fixed to the support arm 20 and the endportions 16 b are fixed to the head arm 15. In addition, pivot pins 18are provided on the support arm in such a way as to support the position21 corresponding to the center of mass of the integrated portionincluding the magnetic head slider and other parts, as is the case withthe first embodiment.

[0049] In this embodiment also, the positions at which the leaf spring16 is attached to the respective arms 15 and 20 are different in thehorizontal direction, as is the case with the first embodiment, so thatthe positions at which tensile forces are created are symmetrical withrespect to the urging position of the pivot pins. Therefore, a momentload will be generated about the pivot pins 18 in the rotation directionfor causing the magnetic head slider 3 to approach the surface of themagnetic disk.

[0050] The process for adjusting the position of the center of mass bymeans of the dummy weights is the same as that in the first embodiment,and the description thereof will be omitted. With the structureaccording to the second embodiment, it is possible to make the structureof the support arm of the VCM simple. Therefore, the assembling processcan be made easier. In addition, the load to the VCM can be reduced.

[0051] As per the above, in the present invention, a dummy weight(s) isadded to a magnetic head slider, a load beam and head arm etc. so thatthe integrated portion including these parts are connected to an arm ata position in the vicinity of its center of mass via an elastic membersuch as a spring, and these parts are supported at a predeterminedposition by a pivot pin. Thus, it is possible to provide a hard diskdrive that can resist an external impact even during the operatingstate.

[0052] While in the above-described embodiments, the load beam and thehead arm are described as separate parts, they may be formed as anintegral part. Specifically; they may be formed by a material the sameas the material of the leaf spring having a U-like shape and the portionof the U-like shape may be formed by punching. Alternatively, the loadbeam and the head arm may be integrally molded with a resin and the leafspring having a U-like shape may be attached to it. In the case in whichthe load beam and other parts are integrally molded, it is preferablethat they are made of a lightweight material that has high rigidity andhigh vibration damping ability.

[0053] While in the above-described embodiments, a leaf spring having aU-like shape serving as an elastic member is used as a joining memberfor joining the support arm with the magnetic head slider and otherparts, the shape of the leaf spring is not limited to this. In otherwords, the shape of the leaf spring may be modified in various ways. Forexample, it may be of a circular shape and portions (or a specificportions) of it may be secured to the support arm and the head arm.Furthermore, the leaf spring may be replaced by various elastic memberssuch as a coil spring or a rubber member. In that case, there is nolimitation for the shape and arrangement of such an elastic member aslong as a pivot pin(s) can be so arranged that it can support themagnetic head and other parts at a position in the vicinity of thecenter of mass without difficulties. The joint member may be formedintegrally with the head arm or the support arm.

[0054] While in the above-described embodiment, the pivot pins areprovided on the support arm, they may be provided on the head arm. Inthat case, the pivot pins would be produced easily by press working etc.with a high degree of flatness. It is preferable that the pivot pins,which determine the distance between the head arm and the support arm,be made of a material having stiffness or rigidity such as a metal.However, from the standpoint of impact resistance, a resin or the likehaving high vibration damping ability may also be preferably used as thematerial for the pivot pins, or coating may be applied on the surface ofthe pivot pins with a resin or the like. In addition, while in theabove-described embodiments, the pivot pins are provided on one side ofeach head arm, they may be provided on both sides. In that case, thepivot pin(s) on one of the sides functions to urge (or bias) the headarm and the pivot pin(s) on the other side serves as a limiter forvibration of the magnetic head slider and other parts, when theyvibrate.

[0055] With implementation of the present invention, it is possible toprovide a suspension, a magnetic head, a head actuator and a magneticrecording apparatus in which a risk of head-crash can be reduced tominimum even if they receives a strong external impact under theoperating state.

What is claimed is:
 1. A head supporting mechanism or a suspensionapparatus comprising: a load beam adapted to be attached with a magnetichead slider at one end; and a head arm, a tip end of said head arm beingjoined with the other end of said load beam; wherein a dummy weight isattached to a rear end of said head arm; a center of mass of a portionincluding all of said magnetic head slider, said load beam, said headarm and said dummy weight coincides with a center of swing movement ofsaid head arm in a radial direction of a recording medium and with acenter of swing movement of said head arm in a direction perpendicularto a recording surface of said recording medium.
 2. A head supportingmechanism or a suspension apparatus according to claim 1, wherein saidload beam and said head arm are joined in such a way that their centerlines in the longitudinal direction coincides with each other, andattachment positions of said dummy weight are respectively arranged tobe symmetrical with respect to said center line, and attachmentpositions of a joining member for joining a voice coil motor forswinging said head arm in the radial direction of said recording mediumwith said head arm are also respectively arranged to be symmetrical withrespect to said center line.
 3. A head supporting mechanism or asuspension apparatus according to claim 1, wherein said load beam andsaid head arm are constructed as a single member.
 4. A head supportingmechanism or a suspension apparatus according to claim 2, wherein saidload beam and said head arm are constructed as a single member.
 5. Ahead supporting mechanism or a suspension apparatus according to claim1, wherein said load beam and said head arm are made of a resin.
 6. Ahead supporting mechanism or a suspension apparatus according to claim2, wherein said load beam and said head arm are made of a resin.
 7. Amagnetic head apparatus comprising: a magnetic head slider; a load beamadapted to be attached with said magnetic head slider at one end; and ahead arm, a tip end of said head arm being joined with the other end ofsaid load beam; wherein a dummy weight is attached to a rear end of saidhead arm; a center of mass of a portion including all of said magnetichead slider, said load beam, said head arm and said dummy weightcoincides with a center of swing movement of said head arm in a radialdirection of a recording medium and with a center of swing movement ofsaid head arm in a direction perpendicular to a recording surface ofsaid recording medium.
 8. A magnetic head apparatus according to claim7, wherein said load beam and said head arm are joined in such a waythat their center lines in the longitudinal direction coincides witheach other, and attachment positions of said dummy weight arerespectively arranged to be symmetrical with respect to said centerline, and attachment positions of a joining member for joining a voicecoil motor for swinging said magnetic head in the radial direction ofsaid recording medium with said head arm are respectively arranged to besymmetrical with respect to said center line.
 9. A magnetic headapparatus according to claim 7, wherein said load beam and said head armare constructed as a single member.
 10. A magnetic head apparatusaccording to claim 8, wherein said load beam and said head arm areconstructed as a single member.
 11. A magnetic head apparatus accordingto claim 7, wherein said load beam and said head arm are made of aresin.
 12. A magnetic head apparatus according to claim 9, wherein saidload beam and said head arm are made of a resin.
 13. A head actuatorcomprising: a magnetic head including a magnetic head slider, a loadbeam adapted to be attached with the magnetic head slider at one end anda head arm a tip end of which is joined with the other end of said loadbeam; and a swing portion of a voice coil motor having a support armthat swingably supports said magnetic head; wherein a dummy weight isattached to a rear end of said head arm, said head arm being joined withsaid support arm via a joining member; said head arm is biased, at acenter of mass of a portion including all of said magnetic head slider,said load beam, said head arm and said dummy weight, in a direction awayfrom said support arm by a pivot pin provided on said support arm, sothat said head arm is supported in such a way that it is spaced fromsaid support arm by a predetermined distance with its substantiallyhorizontal state being maintained.
 14. A head actuator according toclaim 13, wherein said load beam and said head arm are joined in such away that their center lines in the longitudinal direction coincides witheach other, and each of attachment positions of said dummy weight, eachof attachment positions of said joining member and each of biasingpositions of said pivot pin are respectively arranged to be symmetricalwith respect to said center line.
 15. A head actuator according to claim13, wherein said joining member comprises an elastic member.
 16. A headactuator according to claim 15, wherein said elastic member comprises aleaf spring having a U-like shape, a round portion and end portions ofsaid leaf spring are arranged along a center line of said load beam andsaid head arm in their longitudinal direction, said round portion issecured to either one of said support arm and said head arm, and saidend portions are secured to the other one of said support arm and saidhead arm.
 17. A head actuator according to claim 13, wherein said loadbeam and said head arm is constructed as a single member made of aresin.
 18. A magnetic recording apparatus equipped with a magnetic headapparatus according to claim
 7. 19. A magnetic recording apparatusequipped with a magnetic head apparatus according to claim
 8. 20. Amagnetic recording apparatus equipped with a head actuator according toclaim
 13. 21. A magnetic recording apparatus equipped with a headactuator according to claim 14.